Question: $ B = \left[\begin{array}{rrr}4 & 2 & 3 \\ 3 & -1 & -1 \\ 0 & -2 & -1 \\ -2 & 0 & 0\end{array}\right]$ What are the dimensions of matrix $ B$ ?
Answer: The first dimension is the number of rows in the matrix. How many rows does $ B$ have? The second dimension is the number of columns in the matrix. How many columns does $ B$ have? So, $ B$ is a 4 $\times$ 3 matrix.